The present invention relates to a method and apparatus for the withdrawal of threaded dental posts, which were installed in the teeth and have to be removed. More particularly, the invention relates to a method and apparatus for the combined action of drilling into the material around an installed dental post and its extraction.
Dental posts are used to secure different dental items, such as false teeth, fillings or various reconstructions in the tooth. Typically, their insertion involves drilling a bore in the pulp canal of the tooth, the post is then inserted in the root canal by pushing the post into it while rotating it clockwise using a hand tool inserted into the recesses of the head of the post. The post is then further fastened in its bore by the use of dental cement, which firmly secures the post in place.
A dental post includes a threaded rod and head having a larger diameter than the rod. The diameters of the rod come typically come in six sizes. Only the first four sizes ranging in size from approximately from slightly over 1 mm. to 1.6 mm. tend to break. The rod normally has a right screw thread along it and the head is provided with a cross shaped recess to receive a tool by which the post is rotated into its bore.
Frequently, a root canal treatment has to be renewed, or a reconstruction has to be replaced. In such case, the original post has to be removed from the patient's tooth so that a replacement post can be installed in the original bore. Typically, rotating the post counterclockwise with a screwdriver inserted into the cross shape recess in the post's head does this.
Unfortunately, all too often, the head of the post shears off from the post, making the removal of the buried remains of the post extremely difficult and time-consuming work.
The present practice of peripheral drilling and breaking the dental material around the post until it becomes accessible to a pair of pliers or a like and becomes loose enough to enable its release, is undesirable. Despite the need for a simpler and more effective manner of withdrawal of dental posts from the client tooth, very few procedures have been developed.
In U.S. Pat. No. 5,951,286 to Rhodes, a hollow boring device is described. It comprises of a hollow cylindrical bit with cutting teeth at its lower end with a shaft that fits a conventional dental drill at its upper part. The inner diameter of the hollow drill is larger than the diameter of the dental post so it may be rotated around the post and while leaving it intact. The bit cuts a circular groove around the post to loosen the latter from the surrounding matrix until a pair of pliers can pull it out. The removal of the post according to this patent therefore include two stages; the formation of the groove around the post, and pulling out the post with a pair of pliers. If the groove is too shallow, the post will not be loose enough to enable its being pulled out. On the other hand, if the cut is too deep, it will harm the underlying tissue, making this practice undesirable.
In U.S. Pat. No. 5,075,948 due to Maier, a minimum clearance post extraction tool is described comprising an internally threaded coupling rod having an hexagonal periphery for turning by a common wrench and of a threaded screw which is carried within it which has a diameter that is smaller then the diameter of the dental post and which bores its way into the shaft of the post and anchors itself therein. Upon turning the coupling rod, the post shaft travels upwardly within the coupling rod while drawing the post out of his bore. Neither the post itself turns during this operation nor any other mechanism exists, beside pulling force to facilitate its extraction.
Other patents such as U.S. Pat. No. 4,412,822 to Blechner, U.S. Pat. No. 4,954,081 to Williams, and U.S. Pat. No. 3,650,032 to Kestler describe techniques and apparatuses to remove, or to set, dowel posts in dental sets outside the patient's mouth.
It is therefore desired to have a method for the removal of dental posts, preferably such that in which the release of the dental post will proceed with minimum harm to the dental material and be performed with a minimum use of pulling force.